1. Field of the Invention
The present invention relates to optical information recording. In particular it relates to a process for forming an erasable image.
2. Description of the Prior Art
It is known to use energy to record an image by effecting a change in a material. For example, the heat generated by a laser beam can be used to change the properties of many materials to make a visible record. For example, U.S. Pat. No. 3,723,121, describes laser beam recording in a thermochromic material which, in its unexposed state, absorbs, but in its exposed state, transmits the beam. No method of erasing the image is mentioned.
As another example, U.S. Pat. No. 3,636,526 proposes the use of certain amorphous semiconductive materials, such as a selenium alloy or a calcogenide, as typified by Ge.sub.15 Te.sub.81 Sb.sub.2 S.sub.2, As.sub.2 S.sub.3 and As.sub.20 Se.sub.60 Ge.sub.20. When a laser beam is applied to a thin film of such material, voids are formed in the material which provide a visible pattern. It is possible to erase the recorded pattern by heating the material.
U.S. Pat. No. 3,971,874 proposes a recording material having a thin film of a vacuum-deposited tellurium oxide, TeO.sub.x, where x is smaller than 2.0. When irradiated with a laser beam, the thin film of the suboxide undergoes a change from a low optical density state to a high optical density state. However, it is reportedly difficult to erase information recorded on this material.
As another example, U.S. Pat. No. 4,278,734 describes an optical information recording material comprising a thin film of a suboxide of a metal or semimetal of Group IIIB, IVB, VB, or VIB, e.g., TeO.sub.x where x&lt;2.0 or BiO.sub.x where x&lt;1.5, added with up to 50 mole % of S and/or Se. When irradiated with light of relatively low energy density, the thin film exhibits such changes in optical density that information can be optically recorded on it with high contrast ratio. Recorded information can be reproduced by either transmitted light or reflected light and, when desired, can be erased by light irradiation of adequate energy density.
None of these references suggest the method of recording with materials used in accordance with the present invention. Furthermore, the previous materials have one or more drawbacks as recording materials such as low optical sensitivity, low image contrast, difficulty of erasure, expense of manufacture or the inclusion of components which are toxic or costly.